Commercial satellite images obtained by researchers at the James Martin Center for Nonproliferation Studies in Monterey, Calif., show work underway at scores of sites across a grid covering hundreds of square miles of arid terrain in China’s Gansu province. The 119 nearly identical construction sites contain features that mirror those seen at existing launch facilities for China’s arsenal of nuclear-tipped ballistic missiles. The acquisition of more than 100 new missile silos, if completed, would represent a historic shift for China, a country that is believed to possess a relatively modest stockpile of between 250 and 350 nuclear weapons. The actual number of new missiles intended for those silos is unknown but could be much smaller. China has deployed decoy silos in the past. During the Cold War, the United States developed a plan to move its ICBMs across a matrix of silos in a kind of nuclear shell game, to ensure that Soviet war planners could never know exactly where the missiles were at any given time. The construction boom suggests a major effort to bolster the credibility of China’s nuclear deterrent, said researcher Jeffrey Lewis, an expert on China’s nuclear arsenal. Lewis, along with colleague Decker Eveleth, spotted the construction sites after weeks of scrutinizing commercial satellite photos of northwestern China. He described the scale of the project as “incredible.”